Making decisions

By the end of this step your program can do different things depending on the data, and count things that match a rule.

if: only when it's true

An if runs some lines only when a condition is true:

The program checks the conditions top to bottom and runs the first one that's true. Only one branch runs.

Conditions compare values:

Careful: one = stores a value; two (or three) compare. Mixing them up is a classic mistake.

Try it

products = [ {"name": "Trail Tent", "price": 249.99}, {"name": "Camp Mug", "price": 14.50}, {"name": "Headlamp", "price": 39.00}, {"name": "Sleeping Pad", "price": 89.00}, ] # if / elif / else: check the first condition; if it's false, try the next one. for item in products: if item["price"] > 100: print(item["name"], "-> big purchase") elif item["price"] > 20: print(item["name"], "-> mid range") else: print(item["name"], "-> small extra") # Counting: start at 0, add 1 every time the condition is true. cheap = 0 for item in products: if item["price"] < 50: cheap = cheap + 1 print(cheap, "products cost less than $50") # Your turn: count how many products cost between $20 and $100. # Hint: you can combine two conditions with "and".

Output

Press Run (or Ctrl+Enter) to see the output here.

const products = [ { name: "Trail Tent", price: 249.99 }, { name: "Camp Mug", price: 14.5 }, { name: "Headlamp", price: 39.0 }, { name: "Sleeping Pad", price: 89.0 }, ]; // if / else if / else: check the first condition; if it's false, try the next one. for (const item of products) { if (item.price > 100) { console.log(item.name, "-> big purchase"); } else if (item.price > 20) { console.log(item.name, "-> mid range"); } else { console.log(item.name, "-> small extra"); } } // Counting: start at 0, add 1 every time the condition is true. let cheap = 0; for (const item of products) { if (item.price < 50) { cheap = cheap + 1; } } console.log(cheap, "products cost less than $50"); // Your turn: count how many products cost between $20 and $100. // Hint: you can combine two conditions with "&&" (and).

Output

Press Run (or Ctrl+Enter) to see the output here.

Two patterns to take away:

1. Sorting into groups. if / elif / else puts each product in exactly one bucket.
2. Counting. Start a counter at 0; inside the loop, add 1 only when the condition is true. It's the running total from the last step, with an if in front.

The description checker you'll build uses both: is this description too short? If so, count it.

Your turn

At the bottom of either box, count how many products cost between $20 and $100. You should get 2 (the Headlamp and the Sleeping Pad).

Show a hint (1 of 3)